1. Technical Field
Various embodiments of the present invention relate to, for example, a MEMS (Micro Electro Mechanical Systems) device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate.
2. Related Art
For example, in a MEMS device that includes a resonator with capacitance as a functional element, the resonator is airtightly sealed, in a vacuum state, in a cavity formed in a substrate. Also, even in the case of a functional element that does not require airtight vacuum seal, the functional element is airtightly sealed in a cavity so as to prevent the influences of dust, moisture, and the like.
Traditionally, in a case where such a functional element and a semiconductor circuit element are integrated on one semiconductor substrate, a cavity is formed by providing the functional element on the semiconductor substrate and surrounding the functional element with an insulating film and the like. Therefore, a layer(s) above the cavity is not polished, and there is no consideration for the strength of a formation structure of the cavity against mechanical stress caused by polishing.
On the other hand, in a case where a trench is formed in a semiconductor substrate and a cavity is formed in the trench, it is possible to provide an insulating layer on a lid portion covering the cavity and to form wiring on the insulating layer. In order to form wiring on the insulating layer, it is preferable that a surface of the insulating layer provided on the lid portion be planarized by treating the insulating layer by CMP (Chemical Mechanical Polishing). At this time, if a cavity structure does not have a sufficient strength against mechanical stress, there is a possibility that the lid portion deforms and the airtightness of the cavity and the properties of a functional element are impaired.
As related art, JP-A-2009-59941 (paragraphs 0013 and 0014, FIG. 1) discloses an airtight package that can maintain high airtightness of a cavity, which houses a MEMS device, while being small in size and thickness. This airtight package is also high in quality and reliability. In this airtight package, the cavity that houses the MEMS device is formed by joining a MEMS device substrate and an IC substrate to each other via a frame portion.
On the other hand, WO 2008/023826 (Abstract, paragraph 0003, FIG. 5) discloses a semiconductor device in which a cavity space can easily be provided in a specific region in a case where a semiconductor substrate and a supporting member are bonded to each other via an adhesive layer. This semiconductor device includes a semiconductor substrate, a plurality of columnar structures that are formed on the semiconductor substrate and surround a region of the semiconductor substrate where a cavity is to be formed, and a supporting member bonded to a surface of the semiconductor substrate via an adhesive layer and the columnar structures. In this semiconductor device, a device element is sealed in a cavity surrounded by the semiconductor substrate, the columnar structures and the supporting member.
Furthermore, Japanese Patent No. 5192610 (paragraph 0017, FIG. 1) discloses a MEMS device having a structure which prevents stress from being applied to an electrode in a direction in which the electrode comes close to a movable portion when external pressure is applied during resin transfer molding and the like. This MEMS device includes a substrate and a sealing membrane. A movable portion which vibrates mechanically, and an electrode which is positioned close to the movable portion are provided between the substrate and the sealing membrane. The movable portion and the electrode have a region where the movable portion and the electrode overlap each other with a gap in a direction perpendicular to a surface of the substrate. A first cavity and a second cavity which are separated by the electrode are formed between the substrate and the sealing membrane. The first cavity is positioned on aside of the movable portion in the direction perpendicular to the surface of the substrate when viewed from the electrode at the region where the movable portion and the electrode overlap. The second cavity is positioned on a side opposite to the movable portion in the direction perpendicular to the surface of the substrate when viewed from the electrode at the region where the movable portion and the electrode overlap. An inner surface of a side wall in contact with the electrode, of the first cavity, is positioned more inside than an inner surface of a side wall in contact with the electrode, of the second cavity, in a direction parallel to the surface of the substrate.
JP-A-2009-59941 (paragraphs 0013 and 0014, FIG. 1), WO 2008/023826 (abstract, paragraph 0003, FIG. 5) and Japanese Patent No. 5192610 (paragraph 0017, FIG. 1) are examples of related art.
In JP-A-2009-59941 (paragraphs 0013 and 0014, FIG. 1), a plurality of substrates are used to form a cavity. Therefore, a MEMS device and a semiconductor circuit element cannot be integrated on one substrate. On the other hand, in WO 2008/023826 (Abstract, paragraph 0003, FIG. 5) and Japanese Patent No. 5192610 (paragraph 0017, FIG. 1), a cavity is formed on a single substrate. However, they disclose neither formation of a cavity in a trench of a substrate, nor planarization of a surface of an insulating layer formed on a layer(s) above the cavity.